The present invention relates generally to the field of computers, and specifically to a method of altering an operating system to allow it to boot and run from protected media.
Modern personal computers have become complex, and may include a wide variety of peripheral devices and network interfaces. These devices may connect to the computer via a variety of standard interfaces, including the RS-232 Serial Port, Universal Serial Bus (USB), IEEE 1394 (also known as FireWire or i.Link), Small Computer System Interface (SCSI), and various network interfaces such as Token Ring, Ethernet, Bluetooth, IEEE 802.11, or the like. Most of these interfaces require a fully configured and running operating system to provide access to the attached device(s) and/or network(s). As such, data storage devices attached to the computer via these interfaces are a poor choice for use as backup devices for critical system files needed in the event of a computer crash, such as may be caused by a hard drive malfunction, virus infection or other problem that keeps the computer operating system (OS) from successfully running and providing access the to backup device.
Protected, or read-only, media devices, such as CD-ROM and DVD-ROM, have become ubiquitous parts of modern computer systems, with a CD-ROM and/or DVD-ROM drive standard equipment on the vast majority of computers. In addition, CD-ROM and DVD-ROM “burners,” or drives capable of writing data to these traditionally read-only media, have proliferated to the extent that nearly all personal computer manufacturers offer a CD-ROM burner or DVD-ROM burner as standard equipment on the machines they sell. A cost effective means for a computer user to safely archive large quantities of computer programs and data is to use a CD-ROM or DVD-ROM burner and save the data onto Write Once Read Many (WORM) media, or alternatively, a “re-writable” media. In either case, after data has been burned onto the CD-ROM or DVD-ROM and the media session has been closed, the data is protected from any changes and will appear as a read-only disk to the computer's host OS and to the computer user.
While archiving data in a read-only format on protected media is cost effective, it imposes fundamental limitations on the way the archived data may be used. The standard file-system formats used on CD-ROM and DVD-ROM media were designed with characteristics specific to read-only media. For example, they limit direct use of data archived on the media to computer programs that were explicitly written to work with read-only files. As such, programs that rely on native file-system security features unable to directly use files archived on protected media. The read-only characteristics of protected media also preclude many executable programs from running directly from the media. For example, an executable program may need to write temporary files to the directory from which it was started, such as for scratch space, semaphores to synchronize with other programs or threads, alterations to the OS registry, or the like. As one consequence of the inability of many executable programs to run directly from protected media, most modern computer operating systems, which were designed to operate natively on a read-write storage device such as a hard drive, are unable to load and execute from a protected medium.
The inability of operating systems to run from protected media is a serious shortcoming in the field of disaster recovery—booting the computer following a failed or virus-infected primary drive to fix and/or disinfect the failed drive. This is particularly true for modern operating systems such as Microsoft Windows NT/2000/XP. In the early 1990s, the Microsoft Corporation introduced an advanced operating system called Windows NT. This new operating system, along with its new file system called NTFS, introduced the users of personal computers to a new paradigm whereby files that were created on the hard disk of the personal computer were no longer accessible by users of a legacy operating system such as MS-DOS and those versions of Microsoft Windows that were derived from MS-DOS, such as Windows 3x/9x/ME. Furthermore, Windows NT (and it successors) itself could not run from a protected media; thus simply copying the Windows NT operating system to a bootable medium as a disaster recovery option was only feasible when the recovery medium was a second hard drive.
The mid 1990s brought the adoption of the “El Torito” bootable CD-ROM specification, at the same time that CD-ROM burning hardware was becoming increasing available. The El Torito specification, published by Phoenix Technologies of Irvine Calif. and IBM of BocaRaton Fla., available at http://www.phoenix.com/resources/specs-cdrom. pdf and incorporated herein by reference, allows for one or more bootable hard or floppy disk “image” files on a CD-ROM, and concomitant alterations to the computer's ROMBIOS to support the CD-ROM as a bootable device. With the El Torito specification, it became feasible to create bootable disaster recovery CD-ROM disks using legacy operating system components, which (unlike the more modern OSs) could run from the protected media. Disaster recovery solutions thus could only be developed to run under legacy operating systems that could be booted from removable and read-only media.
Disaster recovery software developers continued to pressure Microsoft to provide a version of the non-legacy operating system that could run from protected media. In early 2002, Microsoft released Windows PE, a non-legacy operating system with limited functionality that is designed to boot and run from a CD-ROM disk. In addition to the limited functionality, Windows PE also comes with additional licensing fees for those who which to manufacture bootable CD-ROM disks containing the operating system. While Windows PE does provide a solution for disaster recovery on computer systems running a non-legacy operating system, it is deficient in several respects. Windows PE has limited functionality compared to the full non-legacy OS. It has limited hardware support, and is only offered for use on CD-ROM devices. Windows PE has limited support for running existing applications, and it does not provide writeable free disk space for running applications. Finally, a Windows PE disaster recovery CD-ROM will not contain user-specific configuration information.
Even with a limited operating system that can boot and run from protected media, the inability to write to free disk space is problematic. For example, following a severe virus infection, a user may wish to boot the computer from a disaster recovery disk, and access the Internet to download and execute a particular anti-virus program. This is impossible under an operating system that does not support writeable free disk space.